Conventionally, an agricultural cultivator consists of a frame and a plurality of ground engaging and working tools with some means to connect those tools to the frame. The connection is usually in the form of a spring release mechanism or mount, a shank which runs from the mount to the ground working tool and the tool itself, usually known as a sweep.
Normally, the shank consists of a section of spring steel which is formed to be part of the arc of a circle with flat sections at the top and bottom ends thereof, holes being provided in those ends to connect both the sweep and the mount on the cultivator frame.
This shank is usually rectangular in cross section with the wide dimension thereof set at right angles to the travel of the soil past the cultivator. Several cross sections have been decided on as being more or less standard in the industry. For example, for a field cultivator a shank could be 9/16" thick and 13/4" wide. For a chisel plow, the shank would be approximately 1" thick and 2" wide. Additionally, the ground engaging tools or sweeps have been standardized to fit this type of shank.
The pitch of the sweep while running through the soil has a substantial effect on the force or draft required to pull the unit while running. It has been found that a pitch angle of 0.degree. to 2.degree. requires the least draft. This of course means that the bottom of the sweep is running very close to the flat and is slicing easily through the soil. The greater the pitch angle, the more the tip of the sweep points downwardly. When this occurs, more surface of the sweep is exposed to the soil and this results in a greater amount of soil to move. Additionally, the tip moving downwards can encounter more compacted soil which also requires more force to cultivate. The result of these happenings is increased draft.
Those in the art will appreciate that the draft of an implement has a direct bearing on the size and horse power of the tractor required to pull it and this also has a direct result of more fuel consumed per acre worked. Therefore, a cultivator with less draft requires less power and less fuel to operate than one with higher draft. Preferably therefore a cultivator should be designed so that its sweep pitch in normal operation is as close to 0.degree. as possible.
Numerous types of mounting mechanisms exist to attach a shank to a cultivator frame. These are designed to hold the sweep at a certain angle of attack and then release at a certain pressure if the sweep should strike a rock or other obstruction, so as to protect it and the shank against damage. However, the shank itself, due to its traditional, rectangular cross section and its construction, is, to some extent, flexible.
As the resistance or hardness of the soil increases on the sweep, a typical shank will "spring back". When this happens the pitch of the sweep increases to more of a "tip down" position resulting in more draft. Obviously, this also creates more resistance and the shank flexes back even further. Tests have shown that this "flexing back" of the shank itself can be up to 10.degree. of pitch though around 5.degree. to 6.degree. is more typical.